Pinion starters in which a starter pinion engages with the ring gear of the internal combustion engine by means of a solenoid actuator during the startup operation are already known. When reaching an engaged end position, i.e., when fully meshing with the ring gear of the internal combustion engine, the pinion closes a contact bridge in the solenoid actuator. By closing the contact bridge the electric starter motor is supplied with current. Once the internal combustion engine has been started, the solenoid actuator is switched off, so that the pinion disengages from the ring gear of the combustion engine and the electric starter motor is therefore no longer coupled to the internal combustion engine.
In conventional starters, the solenoid actuator is energized by the nominal current during the startup, so that a constant acceleration is induced in the pinion, and the pinion is therefore abruptly decelerated when reaching the ring gear of the internal combustion engine. Especially in the case of hybrid engines in which the combustion engine is also regularly switched on and off during the operation, the noise generation is consequently high.
To reduce the noise, DE 197 02 321 describes an energization of a solenoid switch in which the acceleration force acting on the pinion can be selectively controlled with the aid of pulse-width modulation. The control described there selectively controls the movement by varying the pulse duty factor of the supplied current in order to achieve a desired engaging movement in this manner. Because of the required high magnetic force, the frequency on which the pulse-width modulation is based must be higher than 20 kHz since the triggering of the solenoid actuator would otherwise produce noise in the audible range. Frequencies of more than 20 kHz are therefore required, which in turn require the inductivity of the plunger relay to be very low in order to permit a selective control. Such a plunger relay controlled in pulse-width modulated manner thus includes a low number of windings and a high wire cross-section in order to be able to generate the required force despite the low number of windings. At the same time, high supply currents are required.